runtime: Implement MVP support for block-based emptyDir

[sprt]

User-facing changes

• Users need to specify the disk sizeLimit via an annotation because K8s doesn't pass the its sizeLimit parameter over CRI, e.g.:

  annotations:
    io.katacontainers.volumes.emptydir_sizelimit.scratch: 1G

Servicing changes

• Add the below flag to containerd config so that containerd forwards the sizeLimit annotation to Kata:

 [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.kata]
   runtime_type = "io.containerd.kata.v2"
   privileged_without_host_devices = true
+  pod_annotations = ["io.katacontainers.volumes.emptydir_sizelimit.*"]

Current gaps with final implementation

• Format fs in the guest instead of host
• Kata config flag to enable block-based emptyDir
• Policy support

Bugs

root@busybox:/scratch# dd if=/dev/zero of=output.bin bs=1M count=80 oflag=direct
command terminated with exit code 255

then df -hT shows virtiofs

Demo

# busy.yaml
apiVersion: v1
kind: Pod
metadata:
  name: busybox
  annotations:
    io.katacontainers.volumes.emptydir_sizelimit.scratch: 1G
spec:
  runtimeClassName: kata
  containers:
  - image: docker.io/library/busybox:latest
    name: container
    command: ["sleep", "inf"]
    volumeMounts:
    - name: scratch
      mountPath: /scratch
  volumes:
  - name: scratch
    emptyDir:
      sizeLimit: 1G # No effect with block-based

Below you notice that the mount source is ext4 (instead of virtiofs today) and the fs type is ext4 (instead of overlay today):

$ kubectl apply -f busy.yaml
pod/busybox created
$ kubectl exec -it busybox -c container -- df -hT | grep scratch
/dev/vdb             ext4          920.3M    260.0K    856.4M   0% /scratch